Potassium channels in the nervous system serve many roles: maintaining the membrane resting potential, regulating cell volume, and tuning the firing properties of a given neuron. Mutations in K+ channels have been reported to cause many neurological diseases. Episodic Ataxia / Myokymia Syndrome Type 1 (EA1) is the only human ataxia known to be caused by dysfunction of a K+ channel. EA1 is an inherited autosomal dominant human neurological disorder that affects both peripheral and central nerve functions. The gene responsible for EA1 has been identified as KCNA1, which encodes the Shaker-like voltage gated potassium channel Kv1.1 in mammals. Mutations in highly conserved residues of KCNA1 that alter the biophysical properties of Kvl.1 channels have been identified in EA1 patients. The conversion of adenosine (A)-to- inosine (I) in pre-mRNAs is a post-transcriptional chemical modification that generates an RNA transcript with a nucleotide sequence different from its gene. We have discovered that the KCNA1 transcript is a target of RNA editing at a very highly conserved position in its coding sequence. RNA editing at this site causes an isoleucine (I) to valine (V) change at a residue important for channel function within the pore-lining $6 domain of Shaker-type K+ channels. Our rationale for proposing to engineer mice with fully edited and fully unedited Kv1.1 alleles stems from the fact that in vitro mutation of the edited isoleucine residue to the smaller alanine residue reduces the affinity of the pore for the blocking particle by more than 400-fold. This results in channels that either fail to inactivate or inactivate incompletely, consequently passing more current than the wild-type channel. In the case of Kv1.1 channel editing, the I to V change introduced by RNA editing also reduces the amino acid side chain volume at this position that conceivably would have functional consequences. The studies outlined below aim to understand the functional consequences of RNA editing of Kv1.1 in the mammalian nervous system.